Successful politicians take positions that people and movements organize around and get out the vote for. But it’s not always clear which positions are rooted in conviction and which are a matter of calculation. Does it matter?

This question is relevant today, since many of the Democrats planning a presidential bid have been out of sync with the party’s progressive base on a range of issues. Sen. Kirsten Gillibrand (D-N.Y.), for instance, is busy distancing herself from herself on immigration, circa 2008, when she called for English to be the official national language and for “the removal of illegal aliens by expanding detention capacity.” Those positions “certainly weren’t empathetic and they were not kind,” Gillibrand said recently.

And Sen. Elizabeth Warren (D-Mass.) has been an aggressive foreign policy hawk on Iran and Israel, once claiming that the first responsibility of Congress is “to protect Americans from terrorism.” But Warren has recently tried to shift left, giving a speech that called for ending the war in Afghanistan and the scaling back of U.S. military commitments.

Their records in these realms are significant red flags. In truth, though, there are plenty of disappointments in the records of all the major candidates. Sen. Kamala Harris (D-Calif.) has been grilled for her time as California’s attorney general during its peak “tough on crime” years, when she resisted the release of prisoners to relieve overcrowding. And, although Sen. Bernie Sanders (I-Vt.) favors cutting the military budget, he faithfully supports the F-35 jet program, a trillion-dollar sinkhole of waste and corruption that creates jobs for Vermont.

No candidate is perfect, and it is a win worth celebrating when erstwhile hawks and centrists like Warren and Gillibrand tack leftward in order to galvanize movements and compete in elections. Ideas must be debated and taken seriously before they can be translated into policy. But can we trust politicians when they claim, conveniently, to see the light?

The question has a quasi-religious undertone, as if trust should be reserved for the truly redeemed. But this is politics, not religion. It’s about power, not purity.

It’s easy to be cynical about candidate platforms and speeches, yet the evidence suggests that political promises usually are not hollow. They actually do guide what politicians do (or attempt to do) with their power.

And that’s one reason the recent rush to the left among the Democratic candidates is so important. It may be strictly rhetorical, given that the party is out of power (except in the House). But it puts them on the record, creates a basis for accountability and shapes their priorities. We should trust their leftward shifts if we understand trust as something provisionally granted. Our goal isn’t to discern the purity of hearts, but to choose the candidate most likely to prioritize and actually push through a broad and aggressive agenda.

That candidate isn’t necessarily the one with the most consistent record. To cite an example from the other side, Donald Trump’s late-life conversion on the abortion issue is deeply suspicious. Yet he couldn’t be more servile to the priorities of antichoice conservatives. And by stacking the courts with far-right judges, he is serving their interests very well.

The politics of abortion is, in fact, exhibit A in the case for pragmatism. In the late 1970s, it was becoming the conservative movement’s most potent organizing weapon— what Medicare for All is right now for progressives. But the GOP’s presidential candidate in 1980, Ronald Reagan, had a less-than-trustworthy record on the issue. He signed a bill in 1967, as governor of California, that expanded abortion rights, and he never showed much personal commitment to evangelical Christianity.

But opposition to abortion was a key part of Reagan’s 1980 campaign (and subsequent presidency), and social conservatives gave him their enthusiastic support.

The payoff? Reagan became the most effective tool in the last half century for advancing not just antichoice politics, but the whole right-wing agenda. He built the movement’s power, and vice versa, with consequences that are still unfolding: hollowedout unions, off-the-charts inequality, a shrinking public sphere and narrowing reproductive rights.

What was truly in Reagan’s heart in the late 1970s, when he courted social conservatives? Was he motivated by genuine antichoice zeal, or just a need for the votes and organizing power that the movement could deliver?

We will never know. Does it really matter?

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Theo Anderson is an In These Times contributing writer. He has a Ph.D. in modern U.S. history from Yale and writes on the intellectual and religious history of conservatism and progressivism in the United States. Follow him on Twitter @Theoanderson7.